1. Field of the Invention
This invention relates to haze-free lubricating oil compositions having an improved viscosity index resulting from the presence of a hydrocarbon polymeric viscosity index improver as well as to the haze-free additive concentrates by means of which said lubricating oil compositions were formulated. In particular, this invention is directed to haze-free lubricating oil compositions and additive packages used in formulating them containing ethylene-propylene copolymer viscosity index improvers and a haze preventing amount of an oil-soluble strong acid.
2. Description of the Prior Art
An important property of a lubricating composition is the rate at which its viscosity changes as a function of temperature. The relationship between the viscosity and temperature is commonly expressed as the viscosity index (V.I). Lubricant compositions which change little in viscosity with variations in temperature have a greater viscosity index than do compositions whose viscosity is materially affected by changes in temperature. One of the major requirements of the lubricating oils is a satisfactory viscosity-temperature characteristic so that the oils will not lose their fluidity but will show an equally good performance within a relatively wide temperature range to which they may be exposed in service.
In addition to refining natural petroleum oils to improve their viscosity index characteristics, it has been common practice to introduce long chained compounds of the nature of linear polymers in order to raise the viscosity index of lubricant compositions. Among the V.I. improvers that have been described in the prior art are included: polyisobutylenes as taught in U.S. Pat. Nos. 2,084,501 and 2,779,753; polyalkylmethacrylates as described in U.S. Pat. No. 3,607,749; copolymers of alkylmethacrylates and styrene as shown in U.S. Pat. No. 3,775,329; hydrogenated butadienestyrene copolymers as shown in U.S. Pat. No. 2,798,853; and copolymers of butadiene, styrene and isoprene as shown in U.S. Pat. No. 3,795,615.
It has now become well known to utilize ethylenealpha olefin copolymers as viscosity index improvers with high thickening potency, relatively low haze and superior shear stability as seen from the following:
Lubricants containing copolymers of ethylene and propylene having from 60 to 80 mole % of ethylene and viscosity-average molecular weight in the range of 10,000 to 200,000 have been described in U.S. Pat. No. 3,551,336;
U.S. Pat. No. 3,522,180 describes a lubricating oil composition containing a viscosity index improver comprising an ethylene-propylene copolymer having an amorphous structure with a number average molecular weight (M.sub.n) of between 10,000 and 40,000 and a propylene content of 20 to 70 mole % and a M.sub.w /M.sub.n of less than about 5 which is said to provide a substantially shear stable blend with improved viscosity index;
U.S. Pat. No. 3,598,738 describes a mineral oil composition containing a viscosity index improver of a class of oil-soluble substantially linear ethylene hydrocarbon copolymers containing 25 to 55 wt. % polymerized ethylene units and from about 75 to 45% of a comonomer selected from the group consisting of unsaturated straight chain monoolefins of 3 to 12 carbon atoms, .OMEGA.-phenyl-1-alkenes of 9 to 10 carbon atoms, norbornenes and unsaturated non-conjugated diolefins of 5 to 8 carbon atoms which results in systems of outstanding shear stability, and
British Pat. No. 1,205,243 describes the preparation of ethylene-propylene copolymers, obtained by direct synthesis, having a measurable degree of side chain branching and (M.sub.n) of between 40,000 and 136,000.
The prior art also discusses the mechanical agitation, churning or other mechanical disruptions of polymeric materials in U.S. Pat. Nos. 2,727,693; 2,776,274; 2,858,299; and 3,503,948. The degradation of the molecular weight of ethylene-propylene copolymers has become useful in the preparation in order to make various grades of polymers having different molecular weights and different thickening efficiencies in the lubricating oil. Such a degraded olefin polymer has been found to be useful when the precursor higher molecular weight ethylene-propylene copolymer has an ethylene content in the range of 40 to 85%, a degree of crystallinity of from about 1 to 25 wt. % and a molecular weight (M.sub.n) of from 20,000 to 200,000 as taught by U.K. Pat. No. 1,397,994.
It is often found during the preparation, processing and storage of these various oil soluble hydrocarbon polymers that a haze develops in their oil concentrates. The source of this haze does not appear to be the same as that haze resulting from incompatibility of the several additives in a lubricating oil additive concentrate (see U.S. Pat. No. 3,897,353 wherein haze resulting from component incompatibility is overcome in a lubricating oil additive concentrate by blending an amorphous ethylene-propylene copolymer with an n-alkyl methacrylate containing polymer having a number average molecular weight between about 30,000 and about 120,000).